Hi guys, Just finish carbonating my Belgian Witbir and it's taste good but smell like sulfur. Is that a fermentation temperature related issue ?
Hydrogen Sulfide (H2S) is produced by the yeast in every fermentation. Sometimes, excess amounts of it are leaked into the beer. Even then, it tends to largely be blown off by the fermentation. Some causes of excess H2S production: - Nitrogen Deficiency - Low Yeast Pitch Rates - Excess SO2 (e.g. from Metabisulfites) How to fix it after the fact: - Time. O2, and/or some trace metals like Copper, in finished beer will react with and decrease H2S - Stir with Copper (last resort) p.s. - @ilanku, you have exactly the same avatar picture as @Ilanko. What are the odds?
Thank you for the valuable information, I have issues login in to my "Ilanko" account THERE FOR I set up new one under "ilanku"
Give it 3-4 weeks. The sulfur will most likely be gone in about that amount of time, with no additional effort required.
Do you understand the chemistry (or is it biochemistry?) for the sulfur reduction process here? If so, could you please explain it? Cheers!
Actually no I don’t fully understand the processes. I just know that it always works, based on lots of experience. Cheers.
Off the top of my head, so somebody check me... H2S + Cu --> CuS + protons H2S + 2 x O2 --> SO4 + protons 2 x H2S + 3 x O2 --> 2 x H2O + 2 x SO2 @dmtaylor aren't you a Chem-E?
I found a few minutes to look into this. As I would have guessed, it appears that sulfur reduction in the late conditioning phase is more a biological effect than direct chemical reactions. Like so many other things, including diacetyl as well as H2S, the yeast is able to uptake or “eat” their byproducts near the end of the fermentation cycle. There has been research on the uptake of H2S. I do not have access and did not review in detail, but here are some links that might help a savvy person get started: https://www.mbaa.com/meetings/archive/2011/Proceedings/Pages/O-4.aspx https://pubmed.ncbi.nlm.nih.gov/18930001/
Interesting stuff from the summary... "It is released from yeast cells during the cell maturation cycle and assimilated during the budding cycle." If that's strictly true, I'm not sure how the very next sentence can be true... "The decrease in beer’s hydrogen sulfide content during late-stage fermentation is attributed both to the purging effect of carbon dioxide and assimilation by yeast." I wonder if those facts are reconciled somewhere in the main presentation that we can't see.
I had the same issue before with a witbier yeast strain. Fermentation had completed, I moved the beer to the keg, pressurized and poured myself the first sample. Shit. Tons of sulfur. Thinking that is was a fermentation issue at the time and thinking that more fermentation would help fix the issue, I made a small simple syrup mixture, cooled it, added it to the keg, and lightly opened the PRV so that off-gassing could occur. A week or two later the sulfur was cleaned up. Not sure if time solved the issue or triggering refermentation did it (or both), but I was happy to have saved that beer and it turned out testing rather well.
